Additive manufacturing techniques and processes generally involve the buildup of one or more materials, e.g., layering, to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including, e.g., freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing techniques may be used to fabricate simple or complex components from a wide variety of materials. For example, a freestanding object may be fabricated from a computer-aided design (CAD) model.
A particular type of additive manufacturing is commonly known as 3D printing. One such process commonly referred to as Fused Deposition Modeling (FDM) or Fused Layer Modeling (FLM) comprises melting a thin layer of thermoplastic material, and applying this material in layers to produce a final part. This is commonly accomplished by passing a continuous thin filament of thermoplastic material through a heated nozzle, or by passing thermoplastic material into an extruder with an attached nozzle, which melts and applies the melted thermoplastic material to a structure being printed, building up the structure. The melted thermoplastic material may be applied to the existing structure in layers, melting and fusing with the existing material (e.g., the previously deposited layers of the melted thermoplastic material of the structure), to produce a solid finished part.
The filament used in the aforementioned process may be produced, for example, using an extruder, which may include a steel extruder screw configured to rotate inside of a heated steel barrel. Thermoplastic material in the form of small pellets may be introduced into one end of the rotating screw. Friction from the rotating screw, combined with heat from the barrel may soften the thermoplastic material, which may then be forced under pressure through a small round opening in a die that is attached to the front of the extruder barrel. In doing so, a “string” of material may be extruded, after which the extruded string of material may be cooled and coiled up for use in a 3D printer or other additive manufacturing system.
Melting a thin filament of material in order to 3D print an item may be a slow process, which may be suitable for producing relatively small items or a limited number of items. The melted filament approach to 3D printing may be too slow to manufacture large items. However, the fundamental process of 3D printing using molten thermoplastic materials may offer advantages for the manufacture of larger parts or a larger number of items.
In some instances, the process of 3D printing a part may involve a two-step process. This two-step process, commonly referred to as near-net-shape, may begin by printing a part to a size slightly larger than needed, e.g., printing using a larger bead, then machining, milling, or routing the part to the final size and shape. The additional time required to trim the part to a final size may be compensated for by the faster printing process.
A common method of additive manufacturing, or 3D printing, may include forming and extruding a bead of flowable material (e.g., molten thermoplastic), applying the bead of material in a strata of layers to form a facsimile of an article, and machining the facsimile to produce an end product. Such a process may be achieved using an extruder mounted on a computer numeric controlled (CNC) machine with controlled motion along at least the x-, y-, and z-axes. In some cases, the flowable material, such as, e.g., molten thermoplastic material, may be infused with a reinforcing material (e.g., strands of fiber or a combination of materials) to enhance the material's strength.
The flowable material, while generally hot and pliable, may be deposited upon a substrate (e.g., a mold), pressed down or otherwise flattened to some extent, and leveled to a consistent thickness, e.g., by means of a tangentially compensated roller. The roller may be mounted in or on a rotatable carriage, which may be operable to maintain the roller in an orientation tangential, e.g., perpendicular, to the deposited material (e.g., a print bead or beads). In some embodiments, the roller may be smooth and/or solid. The flattening process may aid in fusing a new layer of the flowable material to the previously deposited layer of the flowable material. The deposition process may be repeated so that each successive layer of flowable material is deposited upon an existing layer to build up and manufacture a desired component structure. In some instances, an oscillating plate may be used to flatten the bead of flowable material to a desired thickness, thus effecting fusion to the previously deposited layer of flowable material. In order to achieve proper bonding between printed layers, the temperature of the layer being printed upon must cool, and solidify sufficiently to support the pressures generated by the application of a new layer. The layer being printed upon must also be warm enough to fuse with the new layer. When executed properly, the new layer of flowable material may be deposited at a temperature sufficient to allow the new layer to melt and fuse with the new layer, thus producing a solid part.
Some CNC programs may generate a print program including a tool path for each layer using a “slicing process”. The slicing process may divide or “slice” a computer model of the part to be printed into layers. Typically, slicing processes divide a part into layers having approximately the same print parameters. For example, the slicing process may use a constant thickness for each layer, e.g., a thickness approximately equal to the thickness of the print bead. After dividing the part into layers, a tool path for each layer is generated such that the tool path guides the beads of material being deposited to reproduce the shape of each layer. That is, the tool path directs movement of a nozzle for depositing the material in a layer.
During the slicing process, a number of print parameters for each layer may be taken into account such as, e.g., a width and/or a thickness of print bead, a width of the perimeter of the part, a start location and a stop location of an applicator head including the nozzle, an infill pattern, and a print speed. For example, slicing processes typically divide parts into layers having constant print parameters. Such slicing processes may be inefficient and limited. For example, by maintaining all printing parameters constant for every layer of a part, typical slicing programs cannot optimize print parameters of different sections of a part. It may be desirable, however, to produce a part using different print parameters at separate areas of the part, e.g., printing, an outside perimeter of the part with print beads having dimensions different from the print beads used to form the internal structures of the part.